Induction apparatus



Aug. 11, 1942. w c 2,292,809

INDUCTION APPARATUS Filed'oct. 31, 1940 Inventor: Douglas? W lch,

His Attorney.

Patented Aug. 11, 1942 UNITED STATES PATENT OFFICE mnUc'rroN APPARATUSDouglas F. Welch, Rugby, England, assignor to General Electric Company,

New York a corporation of Application October 31, 1940, Serial No.363,765

. In Great Britain February 28, 1940 4 Claims.

My invention relates to induction apparatus having particularapplication to electric ignition systems for internal combustionengines.

An object of my invention is to provide induc- .tion apparatus such thata maximum voltage breakdown of the spark plug gap.

My invention will be more fully set forth in the following descriptionreferring to the accompanying drawing, and the features of novelty whichcharacterize my invention will be pointed out in the claims annexed toand forming a part of this specification.

In the drawing the single figure diagrammatically illustrates a magnetofor electric ignition systems which is provided with an embodiment of myinvention.

In the application of induction apparatus, such as magnetos or inductioncoils, to electric ignitiou apparatus for internal combustion engines,it is desirable to obtain the largest voltage across the high voltageterminals for a minimum current which is interrupted by the breaker inthe primary winding circuit. I have found that this result will obtainwhen the coupling coefficient between, the primary and secondarywindings is of a value of substantially 0.8, or more particularlybetween 0.75 and 0.85. With a coupling coeflicient having such a value,the peak of the resultant secondary voltage wave occurs somewhat earlierthan the peak of the low frequency component.

The coupling coeffici sion V L1XL2 where M is the mutual inductance andL1 and Lo inductances oi the primary and secondary nt is given by theexpreswindings respectively.

Referring to the drawing, I have illustrated a conventional circuithaving a magneto which is provided to obtain electric ignition for aninternal combustion engine. This ignition apparatus of the internalcombustion engine.

numeral l0 having a primary winding H and a secondary winding l2. Inorder to alternate the flux linking the coils a core i3 is provided withan inductor M which rotates in synchronism,

with the rotation of the crank shaft or cam shaft In order toperiodically short-circuit the primary winding,

it is connected through the cables l5 and I6 across a breaker havingcontacts l1 and I8 and an actuating arrangement for the movable contactarm ll such as a cam l9 which is also operated in synchronism with themovement of the crank shaft or the cam shaft of the internal combustionengine. The breaker is also shunted with the conventional condenser 20and 'one side of the breaker is grounded. One side of the secondarywinding I2 is connected to a distributor 2| which will in turndistribute the electric ignition impulse to the spark plugs in thecylinders of the internal combustion engine in proper timed relation.One spark plug is indicated by the numeral 22. One terminal of the sparkplug is of course grounded and the secondary winding I2 is connected toone side of the primary winding ll' through the cable 23 so as to form acomplete circuit.

If all the flux produced by the primary ing were to link the secondarywinding, the coupling coeflicient is equal to one. However, since allthe flux of the primary winding does not link the secondary winding thecoupling coefficient is of a value less than one. I have found thatsubstantially the largest voltage will appear across the secondaryterminals for a given or' predetermined interrupted primary current whenthe coupling coefllcient between the primary and secondary windings isin the neighborhood of .80, or between .75 and .85. The coupling ootheform of a part turn, a whole turn or even includes a magneto indicatedgenerally by the eflicientcan be so made, in any desired manner, such asby placing between the primary wind- .ing II and the secondary windingl2 a magnetic shunt 24. This magnetic shunt comprises a sheet ofmagnetic material, such as iron, which is between-the primary andsecondary windings and concentric therewith. This shunt may take severalinsulated turns of a strip of magnetic material of suitable thickness.This thickness together with the width of the shunt determines theextent to which the coupling coefllcient is affected. It is, therefore,possible for the width of the shuntto be equal to, greater than, or lessthan the length of the coil former, depending upon the thickness and thenumber 0! turns of the material used. It is also possible for thewindshunt to take the form of one or more layers or part layers, woimdwith wire having magnetic properties. The shunt could then, if desired,

form a portion of one of the windings. The reduction of the couplingcoeflicient may also be efl'ected by including a suitable inductance inseries with the primary or secondary windings, or both. The transformermay also be an auto transformer.

In view of the foregoing it will be seen that I have provided anarrangement for obtainingthe largest voltage across the secondaryterminals of an induction apparatus for a given primary current. Myinvention, although not limited thereto, is particularly suitable for anelectric ignition apparatus such as a magneto or an induction coil. ThusI provide that the coupling coeflicient between the windings is lessthan one, or in the neighborhood of 0.80, This desired couplingcoefficient may be obtained in any suitable manner and in addition toobtaining the desired secondary voltage wave form, this particularcoupling coefficient also reduces the duration of the secondary currentbetween the desired sparks.

Although I have shown and described particular embodiments of myinvention,--I 'do not desire to be limited to the particular embodimentsdescribed, and I intend in the appended claims to cover allmodifications which do not depart from the spirit and scope of myinvention."

What I claim as new and desire to secure by Letters Patent of the-United States:

1. An ignition circuit for producing ignition for an internal combustionengine having an induction apparatus including primary and secondarywindings, a breaker connected with said primary winding, and means forproviding a coupling coeflicient between said primary and said secondarywindings having a value between .75 and .85 so that a substantiallymaximum voltage is obtained across said secondary winding for apredetermined current interruption by said primary winding breaker.

2. An ignition circuit for producing ignition for an internal combustionengine having an induction apparatus including primary and secondarywindings, a breaker connected with said primary winding, and means forproviding a coupling coeflicient between said primary and secondwindings having a value in the neighborhood of .80 so that asubstantially maximum voltage is obtained across said secondary windingfor a predetermined current interruption by said primary windingbreaker.

3. An ignition circuit for producing ignition for an internal combustionengine having an induction apparatus including primary and secondarywindings, a breaker connected with said primary winding, and amagnetizable material between said windings and of such dimension incomparison with said windings that the coupling coefficient therebetweenwill have a value of in theneighborhood of .80 so that a substantiallymaximum voltage is obtained across said secondary winding for apredetermined current interruption by said primarywinding breaker.

4. A magneto including primary and secondary windings,'means forinterrupting said primary winding circuit, and means including amagnetizable material between said primary and secondary windings forproviding a coupling coeflicient of said primary and secondary windingsof substantially .8. I

DOUGLAS F. WELCH.

